The purpose is to determine the brain organization and inter- dependence between speech production, speech perception and language in adults. CT scan data from the Vietnam Head Injury Study provide information on lesion topography following penetrating missile wounds. These studies continue to demonstrate the importance of subcortical white matter traits in the left hemisphere for speech and language recovery. Recovery patterns suggest considerable plasticity when lesions only involve the cortical speech and language areas. Some speech functions, such as rhythm and rate, are affected by unilateral lesions in subcortical structures of the left or right hemispheres. Therefore, the neurological control of some aspects of speech production are separate from language. Similarly, in speech perception, only the perception of the temporal order of speech sounds was associated with lesions in the left hemisphere but the identification of rapid stop gaps was not. Positron emission tomography is being conducted in normal volunteers after performing a psychophysical test of temporal order perception for speech sounds. The aim is to determine whether performance is related to increased metabolism in the left temporal region.